[PATCH 2/3] selftests/proc: ensure the test is performed at the right page boundary

[Suren Baghdasaryan <surenb@google.com>]

When running tearing tests we need to ensure the pages we use include
VMAs that were mapped by the child process for this test. Currently we
always use the first two pages, checking VMAs at their boundaries and
this works, however once we add tests for /proc/pid/smaps, the first two
pages might not contain the VMAs that child modifies.
Locate the page that contains the first VMA mapped by the child and use
that and the next page for the test.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 tools/testing/selftests/proc/proc-maps-race.c | 78 ++++++++++++++++---
 1 file changed, 68 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/proc/proc-maps-race.c b/tools/testing/selftests/proc/proc-maps-race.c
index a734553718da..c5031b0593b7 100644
--- a/tools/testing/selftests/proc/proc-maps-race.c
+++ b/tools/testing/selftests/proc/proc-maps-race.c
@@ -39,6 +39,13 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 
+#define min(a, b) \
+	({ \
+		typeof(a) _a = (a); \
+		typeof(b) _b = (b); \
+		_a < _b ? _a : _b; \
+	})
+
 /* /proc/pid/maps parsing routines */
 struct page_content {
 	char *data;
@@ -77,6 +84,7 @@ FIXTURE(proc_maps_race)
 	struct line_content first_line;
 	unsigned long duration_sec;
 	int shared_mem_size;
+	int skip_pages;
 	int page_size;
 	int vma_count;
 	bool verbose;
@@ -105,27 +113,68 @@ struct vma_modifier_info {
 	void *child_mapped_addr[];
 };
 
-
-static bool read_two_pages(FIXTURE_DATA(proc_maps_race) *self)
+static bool read_page(FIXTURE_DATA(proc_maps_race) *self,
+		      struct page_content *page)
 {
 	ssize_t  bytes_read;
 
-	if (lseek(self->maps_fd, 0, SEEK_SET) < 0)
+	bytes_read = read(self->maps_fd, page->data, self->page_size);
+	if (bytes_read <= 0)
 		return false;
 
-	bytes_read = read(self->maps_fd, self->page1.data, self->page_size);
-	if (bytes_read <= 0)
+	/* Make sure data always ends with a newline character. */
+	if (page->data[bytes_read - 1] != '\n')
 		return false;
 
-	self->page1.size = bytes_read;
+	page->size = bytes_read;
 
-	bytes_read = read(self->maps_fd, self->page2.data, self->page_size);
-	if (bytes_read <= 0)
+	return true;
+}
+
+static int locate_containing_page(FIXTURE_DATA(proc_maps_race) *self,
+				  unsigned long addr, unsigned long size)
+{
+	unsigned long start, end;
+	int page = 0;
+
+	if (lseek(self->maps_fd, 0, SEEK_SET) < 0)
+		return -1;
+
+	while (true) {
+		char *curr_pos;
+		char *end_pos;
+
+		if (!read_page(self, &self->page1))
+			return -1;
+
+		curr_pos = self->page1.data;
+		end_pos = self->page1.data + self->page1.size;
+		while (curr_pos < end_pos) {
+			if (sscanf(curr_pos, "%lx-%lx", &start, &end) == 2 &&
+			    start == addr && end == addr + size)
+				return page;
+
+			curr_pos = strchr(curr_pos, '\n');
+			if (!curr_pos)
+				break;
+			curr_pos++;
+		}
+		page++;
+	}
+
+	return 0;
+}
+
+static bool read_two_pages(FIXTURE_DATA(proc_maps_race) *self)
+{
+	if (lseek(self->maps_fd, 0, SEEK_SET) < 0)
 		return false;
 
-	self->page2.size = bytes_read;
+	for (int i = 0; i < self->skip_pages; i++)
+		if (!read_page(self, &self->page1))
+			return false;
 
-	return true;
+	return read_page(self, &self->page1) && read_page(self, &self->page2);
 }
 
 static void copy_first_line(struct page_content *page, char *first_line)
@@ -418,6 +467,8 @@ FIXTURE_SETUP(proc_maps_race)
 	struct vma_modifier_info *mod_info;
 	pthread_mutexattr_t mutex_attr;
 	pthread_condattr_t cond_attr;
+	unsigned long first_map_addr;
+	unsigned long last_map_addr;
 	unsigned long duration_sec;
 	char fname[32];
 
@@ -502,6 +553,13 @@ FIXTURE_SETUP(proc_maps_race)
 	self->page2.data = malloc(self->page_size);
 	ASSERT_NE(self->page2.data, NULL);
 
+	first_map_addr = (unsigned long)mod_info->child_mapped_addr[0];
+	last_map_addr = (unsigned long)mod_info->child_mapped_addr[mod_info->vma_count - 1];
+
+	self->skip_pages = locate_containing_page(self,
+					min(first_map_addr, last_map_addr),
+					self->page_size * 3);
+	ASSERT_NE(self->skip_pages, -1);
 	ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line));
 
 	/*
-- 
2.54.0.545.g6539524ca2-goog